Fluorinated aluminas are well known as fluorination or chlorofluorination catalysts. For example the use of both aluminum fluoride and nickel for fluorination or chlorofluorination reactions is described in U.S. Pat. No. 3,650,987. The fluorided alumina is often prepared by the addition of HF to Al.sub.2 O.sub.3. The products from these reactions contain large Amounts of the symmetrical isomers of various chlorofluorocarbons. The addition of metal dopants increases the amount of symmetrical isomers.
German (DDR) Patent Specification 117,580 discloses a process for the preparation of asymmetrical fluorochlorocarbon compounds of the C.sub.2 series (e.g. CFC-114a) by the reaction of tetrachloroethylene, chlorine and hydrogen fluoride over a metal doped aluminum fluoride catalyst. In the example of this patent with the highest amount of asymmetrical products, the 1,1-dichloro-1,2,2,2-tetrafluoroethane (CFC-114a)/1,2-dichloro-1,1,2,2-tetra-fluoroethane (CFC-114) ratio is about 11.5; and the 1,1,1-trichloro-2,2,2-trifluoroethane (CFC-113a)/1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113) ratio is about 8.0. However 57.4% of the product is chloropentafluoroethane (CFC-115), which is generally considered an undesirable byproduct in CFC-114a manufacturing processes. In another example where 6.1% of the product is CFC-115, the ratios of CFC-114a/CFC-114 and CFC-113a/CFC-113 are 7.3 and 3.8 respectively.
European Patent Application 317,981 discloses a process for isomerizing CFC-113 to CFC-113a followed by fluorination with HF to produce CFC-114a. In the example of this patent with the highest ratio of CFC-114a/CFC-114 (52.7) the ratio of CFC-113a/CFC-113 is 1.1. In other examples the CFC-114a/CFC-114 ratio varied from 45.3 to 5.5 and the CFC-113a/CFC-113 ratio from 6.2 to 1.1.
Japanese Kokai 1-172347 discloses a process for the preparation of CFC-114a by first disproportionating CFC-114 to CFC-113a followed by reaction with HF. In the examples the CFC-114a/CFC-114 ratios vary from 9.0 to 16.7 and the CFC-113a/CFC-113 ratios from 0.1 to &gt;36. In the high 113a/113 ratio example the yield of 114a is only 15.0%. In the other examples the yields of 114a varied from 43.0% to 51.0%.
It is also known in the art (GB 1,578,933) that both CClF.sub.2 CClF.sub.2 (CFC-114) and CF.sub.3 CCl.sub.2 F (CFC-114a) may be hydrogenated over a Pd catalyst to CHF.sub.2 CHF.sub.2 (HFC-134) and CF.sub.3 CH.sub.2 F (HFC-134a) respectively. The latter compound (HFC-134a) is considered a refrigerant suitable for replacing CCl.sub.2 F.sub.2 since it does not significantly contribute to stratospheric ozone depletion while CCl.sub.2 F.sub.2 is suspected of being a major contributor.
Accordingly, there is continued interest in developing economic and efficient processes for preparing 1,1-dichloro-1,2,2,2-tetrafluoroethane.